Ophthalmic display comprising an ophthalmic lens and an optical imager

ABSTRACT

The invention relates to an ophthalmic display comprising an ophthalmic lens containing an optical imager insert ( 400 ) presenting a direction of polarization and serving to shape light beams and direct them towards the eye of the wearer to enable information content (I) to be viewed, the display also comprising at least one polarizer element for placing on a face of the lens. According to the invention, said polarizer element is constituted by an element ( 2 A,  2 B) having adjustable polarization.

RELATED APPLICATIONS

This application is a National Phase Application of PCT/FR2005/050829,filed on Oct. 7, 2005, which in turn claims the benefit of priority fromFrench Patent Application No. 04 52541, filed on Nov. 5, 2004, theentirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an ophthalmic display comprising anophthalmic lens and an optical imager enabling information of the imageor the multimedia type to be projected.

BACKGROUND

The term “lens” relates in particular to an optionally-correcting lenssuitable for mounting in the frame of a pair of eyeglasses. Such anophthalmic lens can present conventional eyesight correction,antireflection, anti-dirtying, anti-scratching functions, for example.

U.S. Pat. No. 5,886,822 discloses an ophthalmic lens presenting aprojection insert. Such a projection insert is constituted by an opticalimager for shaping light beams coming from an electronic and opticalsystem that generates light beams from an electronic signal of theminiature screen, laser diode, or light-emitting diode (LED) type. Theoptical imager directs the light beams towards the eye of the wearer toenable the information content thereof to be viewed.

FIG. 1 is a plan view of such a known ophthalmic display.

In the lens 300 there is embedded an imager 400 constituted by a prism401A, a backing prism 401B, a quarterwave plate 404, and a Mangin mirror403. The combiner includes polarization separation treatment 402 thatcan be implemented in the form of a deposit of thin layers.

An electronic signal conveying information is delivered to a miniaturescreen by a cable that is not shown. The miniature screen 320 isilluminated by a back-lighting projector, and responds to this signal bygenerating a pixallized image corresponding to the information.

A light beam coming from the miniature screen and following a path thatis represented by a dashed line is transmitted via a lens 360 and amirror 325 within the ophthalmic lens inside which it passes to reachthe polarization separator treatment 402. The polarization of the lightbeam emitted by the screen is oriented in such a manner as to lie in theplane of incidence of light rays on the polarization separator treatment402. It is said to be oriented in the P direction. The light beam thenpropagates through the backing prism 401B, then through the quarterwaveplate 404, and then to the Mangin mirror 403 where it is reflected topass back through the quarterwave plate in the opposite direction. Therole of the Mangin mirror is to produce an enlarged image I of thescreen and to position it in such a manner that is at a comfortableviewing distance for the user. Commonly, this viewing distance isadjusted so that the image appears to the user as though it weresituated 1 meter (m) ahead. Furthermore, the apparent size of the imagemay be about 12° along a diagonal, depending on the characteristics ofthe imager.

The quarterwave plate 104 has its axes oriented at 45° to thepolarization of the light beam. Thus, on the first passage of the lightbeam, it comes out in a circular polarization state. Finally, at the endof the second passage, the light beam is in a linear polarization state,but oriented at 90° to its initial polarization. In this way, when thelight beam reflected by the Mangin mirror 403 has passed a second timethrough the quarterwave plate 404, it encounters the polarizationseparator treatment 402 where it then possesses a polarization directionthat is perpendicular to the plane of incidence, commonly written S. Itis thus reflected with high photometric efficiency to the eye of thewearer who thus sees the enlarged image I of the miniature screen 320via the Mangin mirror 403.

Such a display presents the following problems.

The insert 400 substantially occupies a cube of area equal to thefrontal area of the insert, in which area the view of the environment isdisturbed. Outside the cube, the wearer of the eyeglasses can see thesurroundings through the lens 300.

It is found that the information image I displayed by the system suffersfrom a loss of contrast due to the superposition of light coming fromthe outside environment. This phenomenon is particularly noticeable whenthe information eyeglasses are used outdoors.

Contrast is defined as follows:

C=(I _(on) −I _(off))/(I _(on) +I _(off))

where I_(on) is the intensity received by the eye when looking at aninformation image placed in front of the surroundings, and I_(off) isthe image received by the eye when looking at the surroundings withoutan information image.

Furthermore, the polarization separator cube contained in the lens isvisible from the outside which produces an unattractive appearanceeffect. This is due to the polarization separator multilayer treatmentthat allows only 50% overall of the non-polarized ambient light to passthrough.

OBJECTS AND SUMMARY

The object of the invention is to propose an ophthalmic display enablingthose problems to be solved, by enabling proper contrast to be conservedin the image and by hiding the cube so as to make it as little visibleas possible.

To do this, the invention provides an ophthalmic display comprising anophthalmic lens containing an optical imager insert presenting adirection of polarization and serving to shape light beams and directthem towards the eye of the wearer to enable information content to beviewed, the display also comprising at least one polarizer element forplacing on a face of the lens, the display being characterized in thatsaid polarizer element is constituted by an element having adjustablepolarization.

In an embodiment, said polarizer element presents polarizationperpendicular to that of the insert.

Furthermore, in another embodiment, said polarizer element presentspolarization parallel to that of the insert.

Preferably, said polarizer element comprises an active film based onchiral molecules presenting polarization rotation of adjustablemagnitude.

And advantageously, said active film is pixellized, each pixel beingsubjected individually to an electrical signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described below in greater detail with the help offigures that merely show a preferred embodiment of the invention.

FIG. 2 is a diagrammatic view of the invention.

FIG. 3 is a cross-section view of a display in accordance with theinvention, in a particular embodiment.

FIG. 4 shows a display in accordance with the invention, constitutinganother particular embodiment.

DETAILED DESCRIPTION

FIG. 2 shows the lens 300 containing an optical imager insert 400. Byway of example, the optical imager can be of the same type as thatdescribed in above-mentioned U.S. Pat. No. 5,886,822.

The ophthalmic display in accordance with the invention comprises saidophthalmic lens 300 containing an optical imager insert 400 presenting apolarization direction P for the purpose of shaping light beams anddirecting them towards the eye 1 of the user so as to enable informationcontent to be viewed. The display also comprises a polarizer element 2for placing on one of the faces of the lens 300, preferably its frontface.

Such a polarization separator cube 400 presents high transmission for Ppolarization, substantially equal to 90% or more, and low transmissionfor S polarization, and it presents high reflection for the Spolarization, substantially equal to 90% or more, and low reflection forP polarization.

The imager insert 400 is then said to have P polarization, and in thisembodiment, the polarizer 2 presents polarization parallel to that ofthe insert 400.

In this configuration, the alignment of the polarization direction ofthe polarizer 2 with the polarization direction P of the separator cube400 has the effect of making transmission more uniform over the entirelens. The visibility of the multilayer treatment 404 to an outsideobserver is thus greatly diminished.

By way of example, assume that the lens 300 without a polarizer isplaced on a white sheet. Transmission of the surroundings through theremainder of the lens is then substantially equal to 100%, whiletransmission of the surroundings through the cube 400 is substantiallyequal to 50%, in non-polarized light. The separator cube 400 thenappears with contrast equal to 0.33, and is therefore clearly visible.

Now assume that the front face of the lens 300 has the polarizer 2oriented in a polarization direction that is parallel to that of theinsert 400. Transmission of the surroundings through the remainder ofthe lens is substantially equal to 50% and transmission of thesurroundings through the cube 400 is substantially equal to 45%. Theseparator cube 400 then appears with contrast of about 0.05: thatrepresents an object that is hardly visible.

The polarizer element may be constituted by a removable plate that canbe secured to the frame of the eyeglasses by means of a clip suitablefor being secured to the frame by hooks or by magnetic portions.

The polarizer element may be constituted by a film suitable for beingadhesively bonded to the lens in permanent or temporary manner.

The polarizer element may be constituted by layers deposited as films onthe lens. For example, this type of polarizer may be constituted by afilm, brushed molecules, or a wire polarizer of the kind known to theperson skilled in the art.

In a particular embodiment, the polarizer element is constituted by anelement with adjustable polarization. Under such circumstances, it canbe constituted by an active film based on chiral molecules presentingpolarization rotation that is adjustable in magnitude.

Generally, in an adjustable polarization element of that type, a liquidcrystal layer is associated with a conventional polarizer. By applying acontrol voltage, it is possible to vary the orientation of the polarizeras a whole. The polarization orientation control is set by the userusing a control unit. Advantageously, the control unit is integrated ina single housing that provides overall control for the ophthalmicdisplay.

This embodiment presents the advantage of enabling the orientation ofthe polarizer to be adjusted in order to obtain the desired effect.

By setting the polarization direction of the polarizer system parallelto that of the insert 400, the insert 400 as seen from the outsidebecomes camouflaged, as described above.

By adjusting the polarization direction of the polarizer system to beperpendicular to that of the insert 400, the brightness of the image ofthe environment is reduced.

In terms of orders of magnitude, for various lighting conditions, thecontrast of the image I displayed by an information-display lens 300with luminance of about 120 candelas per square meter (cd/m²) isevaluated as shown in the table below, when not using a polarizer inaccordance with the invention.

Contrast of the information image Intense light (painful) <0.01 (0.006)Sunlight <0.05 (0.041) Cloud cover ≈0.06 (0.066) Precision work (CIE≈0.4 (0.383) recommended) Office (CIE recommended) ≈0.6 (0.611) Town atnight ≈0.8 (0.835)

With a polarizer 2 of direction crossed relative to that of theseparator cube 400, transmission through the cube drops considerably.The greater the effectiveness of the polarizer 2 and the better theseparator treatment 402, the better is the improvement in contrast.Ideally, for a polarizer 2 and treatment 402 that are perfect, thecontrast that is obtained is equal to 1.

In the configuration where it is desired to improve the contrast of theinformation image compared with the brightness of the surroundings, thedirection of the polarizer crosses that of the P polarization of thecube 400. Under such circumstances, the transmission of the environmentthrough the remainder of the lens is about 50%, and the transmission ofthe environment through the cube 400 is close to 0.

Estimating that the cube presents efficiency substantially equal to 90%and that the polarizer presents efficiency substantially equal to 99%,then the following contrast values are obtained by means of theinvention.

Contrast of the information image Intense light (painful) ≈0.06 Sunlight≈0.3 Cloud cover ≈0.4 Precision work (CIE ≈0.8 recommended) Office (CIErecommended) ≈0.9 Town at night ≈0.95

Compared with the preceding table, it can be seen that contrast isimproved very significantly, making the equipment easy to use even underoutdoor conditions of the “cloudy cover” type, and possibly even underconditions of “sunlight”.

When the polarizer element is not constituted by an element providingadjustable polarization, it is advantageous for the ophthalmic displayalso to include a second polarizer element presenting polarization thatis perpendicular to that of the insert 400 and that is for placing onone of the faces of the lens 300.

When the device is in use solely as a lens for correcting eyesight, theuser makes use of the first polarizer 2 that serves to camouflage theimager insert 400.

When the device is used as a lens for viewing an information image I bymeans of the imager insert 400, the user makes use, where necessary, ofthe second polarizer that optimizes contrast of the image, even when thebrightness of the surroundings is considerable.

In a particular embodiment shown in FIG. 3, the polarizer element isconstituted by an element having adjustable polarization.

In one type of element having adjustable polarization, a liquid crystallayer 2B is associated with a conventional polarizer 2A. By means of acontrol voltage 3, it is possible to vary the orientation of the overallpolarizer. Control of polarization orientation is set by the user usinga control unit.

In the rest state, no voltage is applied to the liquid crystal film 2B.Thus, the liquid crystals do not transform the polarization of light Lfrom the surroundings passing through the lens.

If the polarizer element has S orientation, then the light L1 from thesurroundings passing through the polarization separator cube takes onthat polarization and becomes blocked by the polarization separatortreatment. The cube 400 appears opaque and then the contrast of theinformation image I is improved over the image of the surroundingbackground.

Conversely, if the polarizer element has P orientation, then the lightL1 from the surroundings passes right through the separator cube 400with transmission that is substantially equivalent to that of the lightL passing through the other portions of the lens. The insert is thusmade poorly visible for an external observer.

In the active state, a voltage V is applied to the liquid crystal film2B. This voltage V is calculated by the means of the art so that theliquid crystals cause the polarization of the light to turn through 90°.Thus, if the polarizer 2A is oriented with P polarization, then at theoutlet from the liquid crystal layer 2B, the polarization will be S; andif the polarizer 2A is oriented with S polarization, then at the outletfrom the liquid crystal layer it will have become P. This providesbehavior that is the opposite of the behavior obtained in the reststate.

Alternatively, it is possible to enable the voltage V to vary,optionally continuously, over the range 0 volts (V) to U V so as tomodulate the rotation imparted to the polarization by the liquidcrystal. This makes it possible to obtain transient behavior so as toobtain a compromise between reduced visibility of the insert and bettercontrast relative to the surroundings, as selected by the user.

As shown in FIG. 4, it is possible to pixellize the liquid crystal films2B so as to be able to modulate the polarization direction locally. Eachpixel is addressed individually with an electric signal serving to turnthe polarization through a known angle. These techniques are known inthe field of liquid crystal display (LCD) screens. This makes itpossible to modulate in space the transmission of the polarization in acontrollable manner. This can be useful for viewing surroundings thatpresent a high degree of polarization (water surfaces, blue sky oppositefrom the sun, reflection off glass, etc. . . . ) under conditions thatcan be selected by the user, while maintaining either aninsert-camouflaging function, or an improved-contrast function.

By way of example, FIG. 4 shows a side reflection from glass, referencedRV, coming from the surroundings. The liquid crystal film 2B has pixelsPI(S) with polarization S and pixels PI(P) with polarization P. Thefirst pixels PI(S) serve to improve contrast relative to theenvironment. The second pixels PI(P) serve to block the reflection RVcoming from the side. The remaining light from the environment isrepresented by arrow L.

1. An ophthalmic display comprising: an ophthalmic lens containing anoptical imager insert presenting a direction of polarization and servingto shape light beams and direct them towards the eye of the wearer toenable information content to be viewed, the display also having atleast one polarizer element for placing on a face of the lens, whereinsaid polarizer element is constituted by an element having adjustablepolarization.
 2. A display according to claim 1, wherein said polarizerelement presents polarization perpendicular to that of the insert.
 3. Adisplay according to claim 1, wherein said polarizer element presentspolarization parallel to that of the insert.
 4. A display according toclaim 1, wherein said polarizer element further comprises an active filmbased on chiral molecules presenting polarization rotation of adjustablemagnitude.
 5. A display according to claim 4, wherein said active filmis pixellized, each pixel being subjected individually to an electricalsignal.